What Causes One Car Headlight to Work While the Other Doesn't?
3 Answers
It could be due to a blown fuse, a short circuit in the bulb, or the bulb burning out. Typically, if only one headlight is not working, it is most likely caused by a burnt-out bulb. If both headlights stop working simultaneously, it might be due to a blown fuse, both bulbs burning out at the same time, or aging and broken wiring or loose terminals. However, the latter two scenarios are extremely rare. Solution: Locate the Fuse Box: The vehicle's circuit fuse box is usually fixed under the hood in the engine compartment, near the fender. The exact location varies depending on the car model. Open the Cover and Inspect: Once you find the circuit fuse box, open its cover. Inside, you will see various fuses and controllers of different amperages for different electronic components. The back of the cover usually has a corresponding diagram to help locate the fuses for the left and right headlights. Use the provided fuse puller to remove the fuse and check if the contact points between the two poles are melted. If there is a gap, the fuse is blown. If the nodes appear normal, reinsert the fuse and proceed to inspect both headlights. It is recommended to visit a 4S dealership for repairs in such cases.
I remember last time when I was driving my old car, the right headlight was on but the left one wasn't, so I quickly checked several areas. The most common issue is a burnt-out bulb—the left side takes more bumps, making the filament prone to breakage. Alternatively, it could be a blown fuse, as cars usually have separate fuses for each headlight. I pulled out my phone to check the manual, located the fuse box, and replaced it with a new one. Poor wiring connections are also common—I felt the bulb socket and found it loose, so tightening it fixed the problem. Short circuits or aging wires are more troublesome, but a multimeter can check if the current is normal. Though rare, rusted sockets or relay failures can also occur. Wiping these components during regular maintenance can prevent most issues—don’t delay, as poor visibility at night can be dangerous.
I often help my neighbors fix their cars, and this issue of one side being bright while the other is dim is usually a minor one. Most likely, it's a burnt-out bulb or a blown fuse—the fuse box is easy to find under the steering wheel or in the corner of the engine bay. Start by trying to replace the bulb yourself; just buy a matching model and screw it in. If that doesn’t work, check if the wire connectors are loose and gently tighten them to avoid breaking the wires. In rare cases, a previous front-end collision might have caused localized circuit damage. By the way, improper headlight height adjustment can also make one side appear dimmer, but it shouldn’t cause complete darkness. In any case, starting with a simple bulb or fuse replacement won’t cost much.
